Sporamin, a storage protein family, accounts for 60-80% of total soluble proteins in the tuberous roots of a sweet potato (Maeshima et al., 1985, Phytochemistry 24: 1899-1902). It is encoded by two major gene subfamilies, A and B (Hatori et al., 1989, Plant Mol Biol 13: 563-572). The genomic DNA of two sporamin genes, SPO-A1 and SPO-B1, have been isolated and characterized (Hattori and Nakamura, 1988, Plant Mol. Biol. 11: 417-426). They belong to the gene subfamilies A and B, respectively.